When a journal article declares “we should expect more from our sewage sludge,” it is hard not to bristle, at least a little, since the authors seem to presume that none of us are doing so. At least, that was my reaction while reading the not-yet-published article with that title in the Journal of Engineering Science and Technology.

This paper by Jordan Peccia and Paul Westerhoff is a “just accepted manuscript,” so is still in a draft /review format. But it is posted to the journal website and can be downloaded for your reading pleasure. The working title is, as I have already said, “We should expect more from our sewage sludge.”

The underlining premise of this paper will sound familiar to those of you on-board with WEF’s new Water Resource Recovery Facility (WRRF) paradigm. Peccia and Westerhoff argue that our WRRFs ought to recover nutrients, metals and energy and yield a residual with no odors, pathogens or persistent pollutants. They urge us to explore basic science and engineering for sustainable solutions and that we justify new public capital investment with triple bottom line, economic and human health based sustainability assessment tools.

How can you disagree?

I do believe many of us are expecting this for the future of our biosolids programs, as we pursue WRRF-appropriate solutions. So I delved into this new paper looking for some new ideas and approaches we may be missing. Three items seemed to be their “new, new ideas:” wet chemical oxidation, hydrothermal liquefaction, and biomimicry.

These were unexpected, as I had expected to read about three different technologies. After all, our industry is embracing such WRRF-compatible approaches as mainstream anaerobic treatment, co-digestion and thermal hydrolysis. But these three popular technologies were eschewed by Peccia and Westerhoff for not advancing the possibility of separating metals, reducing mass and capturing all incoming nutrients. As the authors state, “We do not advocate the continuation of land application, as it has limited social and economic sustainability.” In their view, soil amending with biosolids is not “expecting more.”

The first of their three new ideas, “Wet chemical oxidation,” which I take to be Supercritical Wet Oxidation, or SCWO, may be on the verge of breaking onto the biosolids technology scene. Orange County Sanitation District announced that it was negotiating with SCFI Aquacritox to develop a large pilot facility. The Bay Area Biosolids-to-Energy Coalition has supported a proposal to the California Energy Commission by a Synagro/SCFI team for a demonstration facility.

I can only imagine, or hope, that SCFI has more success with its SCWO system than SuperWater Solutions did in Orlando, Florida, with its system. For six years and $8.5 million, the city of Orlando invested a SCWO facility, with the promise that the city would one-day receive a share of future revenues from SuperWater Solutions of $2.50 / ton of biosolids processed for other customers in perpetuity. The project was suddenly halted by an explosion in March 2014 (“Reactor blowout sidelines Orlando's waste-to-energy hopes”).

While the cause of the SCWO failure is not reported in the Orlando article, the challenges of SCWO have been known among technologists. Phil Marrone, with SAIC in 2012, wrote a review article before this event, “Supercritical Water Oxidation – Current Status of Full-scale Commercial Activity for Waste Destruction.” Marrone detailed the challenges with SCWO, including corrosion and clogging from salt build up. He reported that, as of 2012, only two commercial plants were operating in the world, one in Japan treating PCBs and one in France for small quantities of hazardous industrial waste. Yet the most serious technology company out there for new SCWO facilities, SCFI Aquacritox, is focusing on sewage sludge as its special feedstock. The world is still waiting for its first successful SCWO unit for biosolids.

The challenge we share with SCFI, Orange County and the Bay Area is how public agencies can appropriately balance the risk of technology failure with the potential benefit of a solution that has low regulatory and public relations risks. Was it worth $8.5 million in Florida? What will it be worth to those agencies in the San Francisco and Orange County areas of California? The jury is out.

If “supercritical” has been tough to launch, perhaps “subcritical” isn’t as hard. Peccia and Westerhoff seem to think so, which is why they discussed hydrothermal liquefaction (HTL) for several paragraphs. They explain: “hydrothermal liquefaction (HTL)… converts proteins and carbohydrates into oil, increasing potential energy recovery compared against just lipid extraction. HTL mimics, in a very accelerated manner, the natural production of crude oil from vegetative and other organic matter, which has occurred over millions of year under high temperature and pressure.”

So think, too, participants of the Bay Area Biosolids to Energy Coalition, who are working with WERF to support research into a version of HTL offered by technology company Genifuel. WERF pulled the trigger on the evaluation of HTL in February under its Leaders Innovation Forum for Technology, which they described in LIFT Launches Biosolids to Energy Evaluation Project. The third-party evaluation contractor for this project is Phil Marrone, the expert who authored the review on SCWO, now with Leidos. This will be a good thing, as he is a “main man” in this type of processing.

I did some of my own exploring on whether HTL could be a breakthrough technology. I learned from exploring Google Scholar that, unlike SCWO, HTL is still only laboratory scale and its output product is very complicated. A 2011 journal article “Chemical properties of biocrude oil from the hydrothermal liquefaction of Spirulina algae, swine manure, and digested anaerobic sludge,” concluded “biocrude yields ranged from 9.4% (digested sludge) to 32.6% (Spirulina).” Further, the researchers carefully express their concerns for the output “oil:” “HTL feedstock composition [is important] and highlight the need for better understanding of biocrude chemistries when considering bio-oil uses and upgrading requirements.”

With WERF’s help, perhaps we won’t have to wait 30 years to see if the technology will work and what the character of the biocrude will be. At this point, 30 years is too long for me to wait.

I love the term biomimicry and I fancy myself something of a biomimicrist (is that a word?). But alas, I am not a Certified Biomimicry Profession. I went to the website of the Biomimicry Institute, and checked out its faculty. I saw no one really into sewage as a specialty area. One graduate of the Biomimicry Institute, Tim Albertson, went on for a Master’s degree at the University of Nevada Las Vegas, and has produced a thesis with the engaging title “The Integration of biomimicry into a built environment design process model: An alternative approach towards hydro-infrastructure.” He is a Certified Biomimicry Professional, but he is not working in water resources management. Today he recruits students to the Sustainability Resource Center at Cuesta College, in San Luis Obispo, California.

My own experience with a “natural systems approach” to wastewater treatment was dealing with a proposal to the Philadelphia Water Department that the city purchase a “Restorer” for cleaning the Schuylkill River at the Fairmount Water Works. John Todd, principal of the water resources planning firm Todd Ecological Design, had developed the Restorer as a “living filter,” a type of biomimic of natural water cleansing processes. Todd employed the Restorer full-scale in the city of Fuzhou, China, which had 50 miles of open sewage canals in need of an alternative to conventional collection and treatment for the excreta of 6 million residents. This is not exactly a biomimicry system applicable to US cities.

How might biomimicry be relevant to our planning for sustainable biosolids?

In the words of Peccia and Westerhoff: “the principles of biomimicry …aim to look at how the natural environment at the process, organismal or ecosystem scale deals with managing fluxes of elements and energy when they are present in concentrated forms. … we should extend this to understand how the environment uses low-temperature liquid-based processes to separate and store elements or store energy.”

Ugh? Is that clear?

Try as I might, I could not get Google Scholar to link any biosolids technology to a biomimicry vision using those terms from the Peccia/Westerhoff article.